In general, a motor largely includes a rotor and a stator. Recently, a motor, which is widely used for a drum type washing machine, is a direct-coupled outer rotor type motor wherein the stator is directly coupled to a set of motor and the rotor rotates outside the stator.
Such direct-coupled outer rotor type motors have been disclosed in Japanese Patent Publication Laid-open Nos. 2001-258189, 2002-153604, and 2010-130719 and Korean Patent Nos. 0429239 and 0657660.
According to the conventional practices, the rotor has permanent magnets attached to the inner periphery thereof directly or via other members. However, the coupling process of the rotor to the permanent magnets is very complicated and needs high costs, and even though the coupling process is conducted by means of bonding, the time required for the working is much consumed. Since the magnetic field intensity generated from the rotor is constant, further, the sizes or positions of the permanent magnets should be changed whenever the design components like the number of coil windings of the stator, the change of the size thereof and the change of the material thereof are varied, which causes the adaptability of the rotor to various designs to be substantially low.
So as to problem the above-mentioned problems, accordingly, this inventors have proposed to develop a motor having a new structure where a rotor has electromagnets mounted thereon, in place of the permanent magnets attached thereto.